Option to set locale globally

Setting locale for fmt_* globally

Im using gt increasingly in html reports in Europe, therefore I would like to set the locale globally, for example via an option that switches every standard gt fmt_* to use the locale specified in the option.

That would make (working with) gt code in non-US locales less verbose and reduces the need to use purrr::partial

[rich-iannone]

This is a great idea, thanks!